Publications & Papers

Avalon works closely with academia in developing understanding of borehole seismic principles and applications.

By keeping close ties with specialist academic staff, ASL ensures our products remain innovative and responsive to industry requirements.

  • Orientation of a 3-C VSP Dataset Acquired by Integrated Geophone Sensor and MEMS Inclinometer Devices
    • EAGE Passive Seismic Workshop Proceedings, EarthDoc
    • 19 November 2017

    Authors: William Wills (ASL) Charles Naville (IFPEN), Max Nott-Bower (ASL), Gary Tubridy (ASL)


    This paper seeks to gauge the performance of a new commercial downhole VSP tool electronics module, which has been recently implemented with a 3C solid state inclinometer system called a High Side Indicator . The HSI measures the direction of the pull of gravity and calculates the angles of roll and vertical inclination in each shuttle of the borehole seismic toolstring. By so doing, the VSP tool manufacturer expects to replace the previous gimbal settings systems, which proved voluminous, fragile, inaccurate at low inclination, and mechanically difficult to maintain through the lifetime of a VSP tool, and encourage full 3C processing of all downhole datasets, even those acquired within rig source VSP survey geometries. The first objective of this test was to check that the VSP hardware and acquisition software worked as expected, and secondly to define a minimal field QC procedure which includes at least the roll angle rotation and associated 3C VSP displays. From this the field engineer and the client supervisor can be reassured as soon as possible about the overall VSP data quality and usability for advanced full 3C VSP processing by the geophysicists and interpreters.

  • Triggered or Induced Seismicity; A Long Term Approach
    • GeoExpro Vol. 13 No.3 2017
    • May 1, 2017

    Authors: William Wills (ASL)


    William Wills (Avalon Sciences) briefly summarises some of the long term passive monitoring requirements for the appropriate identification and regulation of human-induced seismicity.
  • Constant and frequency-dependent attenuation from vertical seismic profiles in fractured granite and thinly layered sediment
    • EAGE Paris Conference
    • June 14, 2017

    Authors:  CD. Cantú Bendeck* (School of Environment, University of Leeds), RA. Clark (School of Earth and Environment, University of Leeds), AD. Booth (School of Earth and Environment, University of Leeds), W. Wills (Avalon Sciences Ltd, UK)


    A collaboration between the University of Leeds and ASL, which will be presented on the 14th of June at 16:20 in Room A2.

    Abstract: The seismic quality factor, Q, is generally treated as frequency-independent, yet theory and field evidence suggest it may not be.  We measure constant-Qeff and frequency-dependent Qeff(f), from downgoing direct-P arrivals in VSP data, over a 1000 m-thick granite interval in Cornwall, SW England, and a 700 m-thick interbedded shale-carbonate sequence in the Barents Sea, and find two significant results.

    First, we obtain consistent constant-Qeff and Qeff(f) values, although Qeff(f) values vary smoothly with frequency-specific ‘attenuation peaks’.  In the granite, over 25-90 Hz, constant-Qeff =75±47, and Qeff(f) ≈35-100.  For the sediments, over 15-110 Hz, constant-Qeff=152±40, and Qeff(f) ≈70-200.  We conclude that our Q(f) workflow (using logarithmic decrement of individual frequencies’ amplitudes after geometric spreading corrections, so not imposing an analytic Q(f) form) is workable.

    Second, attenuation in this granite is comparably high to that in these sediments.  The granite has only naturally-occurring fractures, but they appear sufficient to increase attenuation above an intuitively-expected level for crystalline rocks. Well-log-based predictions of 1-D scattering contributions to attenuation, for both datasets, are contradictory between Qscat and Qscat(f). We believe the use of elastic synthetic seismograms could clarify the origins of our measured Qeff and

    Overall, we urge that more Q(f) measurements are made, to support of studies of subsurface petrophysical properties and application of signal-processing tools that account for attenuation in seismic imaging.


  • Challenges of the Deep
    • Oilfield Technology 2015
    • November 1, 2015

    Authors: William Wills (ASL)Joe Killen (ASL)


    This article discusses the requirements and delivery of borehole seismic monitoring within extreme high pressure and temperature borehole environments .
  • Reducing velocity model uncertainty and improving microseismic event location accuracy: crosswell seismic tomography using a repeatable downhole sparker source
    • SEG Beijing 2014 – Borehole Seismic Workshop
    • April 20, 2014

    Authors: William Wills (ASL), Dr. James Verdon (Outer Limits Geophysics)


    This paper demonstrates how a commercial down-hole sparker source can be used to produce crosswell tomography surveys that result in much improved velocity profiles. The paper aims to address the impact of differences between acoustic log and crosswell-derived velocity models acquired from a North Belt Test Well, Texas USA on microseismic event location.
  • Into the Abyss. Borehole Seismic – the technological challenge
    • Geo Expro Volume 9 2012
    • September 1, 2012

    Authors: William Wills (ASL)


    Discussion of some of the principle requirements driving borehole seismic technology innovation.
  • Borehole Seismic – Using multiple stacked geophones
    • International Oil & Gas Engineer Article
    • February 4, 2012
    Authors: William Wills (ASL)


    Discussion of the advantages of employing multiple stacked geophones within a borehole seismic monitoring system in order to accurately map fracture induced microseismic events.
  • Reservoir characterization: microseismics now a key tool
    • National Hydrographic and Seismic Search – August 2009
    • August 1, 2009
    Authors: William Wills (ASL)


    Broad upstream industry article commenting on the increasing use of borehole passive seismic and microseismic monitoring within the oil and gas industry.